Electrical apparatus, devices and equipment are often designed to be modular, redundant and interchangeable so that they are more adaptable to the requirements of the user. If the modular device is an electrical control system then a practical modularity is usually achieved by splitting into passive (interference-resistant) terminal modules and active (and hence interference-prone) subassemblies or electronic modules. The control system function required by the customer is ultimately achieved by linking together a number of terminal modules and electronic modules.
Similarly, the power supply components for the electronic control system are designed to be modular, redundant and interchangeable.
In order to guarantee continuous operation, it must also be possible to replace and fit the interference-prone subassemblies or electronic modules, and the power supply modules (PS modules), under load. The apparatus or parts of the apparatus are therefore not switched off before changing the subassemblies or electronic modules or PS modules (all classed below as a subassembly). If, however, a subassembly is connected, for example, to a terminal module via a circuit in such a way that when plugging in or pulling out the electrical subassembly, sparking at the connector between the electrical subassembly and the terminal module cannot be ruled out, then special design measures need to be provided that prevent such sparking.
One option is to design the locking of the subassembly on the terminal module in such a way that internal disconnection of the subassembly is forced to occur when the locking mechanism is operated. This design must also guarantee that enough time elapses between the internal electrical disconnection and the release of the subassembly for any energy still stored in capacitances or inductances to have decayed away safely. This mechanism must work in reverse when plugging in the electrical subassembly, i.e. the internal connection of the subassembly must not be possible until the plugging-in process is complete.
The older European application with application number 03023213.6 proposes a locking mechanism which satisfies safety requirements for locking subassemblies by means of a catch, in which the electrical contact is forced to open during the plugging-in and pulling-out. The locking mechanism and the necessary disconnection during pulling-out and plugging-in takes place in the subassembly in this solution.
Such a solution cannot be implemented if the subassembly has special design characteristics that make it impossible to integrate in the subassembly the implementation of the catch mechanism and the forced disconnection, for instance the fact that the subassembly is encapsulated or potted.